DESCRIPTION (adapted from application abstract): The proposed research is a longitudinal cohort study of school-aged children to define the epidemiology of group A streptococcal pharyngitis. Students in grades K through 8 will be enrolled and throat cultures obtained twice monthly and with each respiratory illness for three years. GAS isolates will be typed by FIGE to determine relatedness and to define infection, carriage, and recurrences. Samples of saliva will be collected for antibody assays and for use in GAS adherence inhibition assays. Baseline, follow-up, and event-specific (e.g., an episode of respiratory infection) clinical information will be collected and analyzed for associations between these variables and protection from or recurrences of GAS pharyngitis. There are four aims: 1) to define the epidemiology of GAS pharyngitis in children; 2) to determine whether specific M-types protect against subsequent infection by GAS with homologous or heterologous M-types; 3) to correlate clinical features that protect against subsequent GAS pharyngitis; and 4) to determine whether saliva produced after GAS infection interferes with adherence of GAS to pharyngeal cell cultures.